The present invention relates to the utilization of magnetic fields established by means of permanent magnets for use in medical diagnosis, particularly of the human body. Whole-body nuclear magnetic resonance diagnostics has been available in the medical arts for some time. Most or all of the currently known devices provide a field of 1.0 kOe over a working volume of about 0.9 m.sup.3. Nuclear magnetic resonance (NMR) has become an increasingly powerful and convenient tool for both medical diagnostics and for medical research. The use of NMR solves the problems attending many applications where it is desirable that large areas of a patient's body be subjected to scanning more or less simultaneously without the movement of either the patient or of large pieces of equipment, either or both of which could easily cause distortion of the discernible indicia being studied. Towards accomplishing the desired goal of making available large areas of the body for scanning without the movement of either the patient or the equipment, fairly large uniform magnetic fields over body-sized volumes had to be effected. A uniform field of magnetic flux in the order of 1.5 kOe has been found sufficient to accommodate the average human body and to suitably fill the volume in which it is contained for diagnostic procedures. It is also desirable for reasons of safety and convenience in many medical diagnostic and experimental procedures to effect the tests or studies without the application of electrical fields. Of the three basic types of purely magnetic systems (resistive, permanent magnet, and superconductive), studies indicate that the permanent magnet type yields the best magnetic field/cost ratio in the relatively low field (1.5-3.0 kOe) regime. Ferrite permanent magnet type NMR diagnostic devices have been constructed and, while found to be suitable for the intended use within a reasonable degree, have been disadvantaged by the heavy weight of the large magnets required to generate the requisite fields over working volumes approximating the size of the human body.
The utilization of ferrite permanent magnets for the construction of nuclear resonance diagnostic devices is also, consequently, quite expensive due to the necessecity for increased support structures, movement and installation, rigging costs and the like before the devices can be put into effective utilization.
In several earlier inventions, notably, U.S. Pat. No. 4,654,618, Mar. 31, 1987 and, U.S. Pat. No. 4,658,228, Apr. 14, 1987, the utilization of rare earth permanent magnetic materials for the effective containment and control without any substantial loss of field flux of electron beams in miniaturized magnetic devices in communications circuits and the like is taught. The '228 patent discusses the confinement of longitudinal axially symmetric magnetic fields and confining these fields with great precision to annular regions within permanent magnet structures. The '618 patent teaches the confinement of magnetic fields to very small areas in miniature devices. Both of these teach the basic concept of using particularly formed and especially shaped tapering in thickness from the ends of the structures to the centers thereof cladding magnets and the use of rare earth compound materials as effective magnetic substitutes for straight ferrites.
The basic teachings concerning the methods by which rare earth materials are put into place in magnetic elements and devices and which are described in detail in the two aforementioned patents, are incorporated by reference as teachings in this disclosure.
With this then being the state of the art, we conceived and developed the present invention to provide for effective NMR diagnostic procedures on relatively large target areas or zones approximating the size of the human body and, particularly, to do this with less bulky and lighter materials than heretofore used in devices of this type.
It is, therefore, a primary object of the present invention to provide an apparatus which may be used for NMR diagnosis of the human body in a particular zone by means of a surrounding rare earth magnetic device particularly constructed so as to align the field flux and effect the passage of same through the target body in a preselected desired manner.
It is a further object of this invention to provide such NMR diagnostic apparatus without the employment of large, bulky, and heavy ferrite devices heretofore used and with the consequent and attendant large structures and supports associated with these devices.
It is further an important object of the invention to provide for the NMR diagnostic procedures on the human body without the employment of electromagnetic fields such as would occur when solenoids, thyratrons, solid state devices, and the like radiation producing elements would be used in heretofore commonly known and available diagnostic machinery.